The present invention relates to power supply systems and, more specifically to a power supply system for use with an automotive vehicle incorporating a reactor for the plasma-assisted treatment of the exhaust gases from its associated engine to reduce the emissions of one or more of nitrogenous oxides, particulate including carbonaceous particulate, hydrocarbons including polyaromatic hydrocarbons, carbon monoxide and other regulated or unregulated combustion products therefrom.
The principles of an arrangement for controlling corona discharge reactions in a corona discharge pollutant destruction apparatus employing one or more corona discharge reactors in a motor vehicle are described in U.S. Pat. No. 5,822,981. NOx, HC (hydrocarbon) and CO remaining in exhaust emissions emerging from the corona discharge reactor are sensed and a computer uses data from these sensors and other engine sensors to provide automatic control of power sources which supply the corona discharge reactors to adjust the power generation parameters to minimise the amount of pollutants in the treated gas. The power sources are, however, only shown indicatively in block diagrammatic form with no details of their components or how they are driven.
Modern motor vehicles include more and more electrical equipment, some of which, such as electronic braking, electronic valve timing and electrically operated power assisted steering systems consume considerable amounts of power and require heavy cables if the transmission power losses are to be kept to a reasonable level when operating with conventional 12 volt or 24 volt battery technology. It should be appreciated that in the automotive industry the principal battery technology is the lead-acid battery system with a nominal 12 volt output and open circuit voltage of 13.2 volts. The charging voltage required for a lead-acid battery is temperature-dependent but typically varies between 13.6-13.8 volts that is a nominal 14 volts due to the open circuit voltage of the battery. For the purposes of this specification we will use the industry adopted terminology of referring to battery voltages in multiples of the nominal 12 volts and to alternator outputs and charging voltages as multiples of the nominal 14 volts. As battery technology develops differing open circuit and charging voltages will apply and it will be it will be appreciated that the present invention is applicable to different battery voltages from those specifically referred to in the examples described in this specification. Power losses increase as the square of the electric currents flowing in the cables and vehicle manufacturers are considering the introduction of higher voltage standards such as 42 volts or 56 volts for charging of 36 volts and 48 volt batteries. In the interim period due to the large number of 12/14 volt systems in service dual voltage power systems are likely to be employed with two or more batteries allowing lower power demand equipment operating at twelve volts as at present and higher power demand equipment operating at thirty six, or even forty eight volts. This situation will be exacerbated when reactors for the plasma-assisted treatment of engine exhaust gases are fitted because such devices have a potential for high additional electrical power demand under certain engine load conditions.
Power requirements can be illustrated by the example in which applying 25 J per liter of exhaust gas flow to process the exhaust from a 250 kW truck engine at full rated power would require approximately 6.25 kW. While this represents an acceptable 2.5% of rated power, it presents a significant challenge as all of the power must be derived from the vehicle electrical power system. No single piece of electrical equipment on a vehicle today represents a challenge of this magnitude. Transmission of 6.25 kW at 12 volts involves currents of 521 amps whereas transmission at 36 volts requires 174 amps and at 48 volts, 130 amps. However, at higher voltages such as 72 or 96 volts, currents are lowered significantly to 87 amp and 65 amp respectively. It is desirable therefore to operate at the highest safe voltage when very high power loading is anticipated. It is generally recognised that operating voltages less than or equal to 50 volts are considered safe and acceptable on vehicles and this is driving the standard of 42 volts or 56 volts charging of 36 volt or 48 volt batteries discussed earlier. It can be seen however from the previous example that in some cases even higher voltages may be required to ensure efficient power transmission to potentially high power demand systems such as plasma assisted emission control. In addition vehicle applications based on use of three or even four output voltage sources in a vehicle are also of interest to motor manufacturers.
Unlike other vehicle power demands it is not necessary to run an emissions after treatment systems when there are no emissions from the vehicle, that is, when the engine is switched off and therefore there is no need to be able to operate the system from the conventional vehicle electrical supply incorporating the battery. An added benefit of this approach is that the absence of the battery in the circuit supplying the emissions control system enables less stringent regulation of voltage to be employed. An economic benefit, that is, lower cost can arise from this feature.
It is an object of the invention to provide a multiple-voltage power supply system for use in automotive vehicles, in particular in a power generation and supply system which is capable of powering plasma-assisted emissions control systems or other high power demand equipment, and in which, together with control functions, the problems of safe and efficient operation are addressed.
According to the invention there is provided a power supply system for a motor vehicle incorporating a reactor for the plasma assisted treatment of exhaust gases from an engine of the vehicle to remove noxious combustion products therefrom, a high voltage power supply adapted to produce an output voltage sufficient to produce a plasma in exhaust gases from the engine of the vehicle as they pass through the said reactor, an engine management system and a power management system adapted to monitor operating parameters of the engine (such as engine speed, throttle position, exhaust gas temperature, engine temperature), including the concentrations of the said noxious combustion products in the exhaust gases, characterised in that there is provided in combination a plural-voltage generator adapted to produce a first output voltage suitable for the operation of lower power demand electrical equipment of the vehicle and a second output voltage which is higher than the first output voltage, the said plural-voltage generator being connected to apply the second output voltage to the high voltage power supply which generates therefrom the said output voltage sufficient to produce a plasma in the exhaust gases, said engine and power management systems being adapted to monitor concentrations of noxious combustion products at both the inlet and outlet ports of the reactor, and to vary a control variable of the high voltage power supply so as to adjust the power supplied to the reactor to minimise the concentrations of the said noxious combustion products in the effluent from the reactor. In this way the overall processing efficiency of the system is increased.
In some situations it will not be possible or desirable to install on-board emissions monitoring of exhaust gas components. In these cases the existing engine sensors would be used to determine, via pre-programmed engine maps in the engine control unit, the levels of emissions for a given engine load/speed combination. In addition it will not always be possible or desirable to install a separate power management system and in such cases the hardware and software would be incorporated into the engine management system.
Preferably the plural-voltage generator is adapted to produce a second output voltage which is a multiple of the first output voltage.
Preferably the high voltage power supply includes an oscillator controlled by the engine and power management systems to adjust the power supplied to the reactor.
Preferably the high voltage power supply further includes a transformer to which the output of the oscillator is connected.
Preferably the first output voltage of the generator is a nominal 14 volts, and preferably the higher voltage output is produced as an alternating voltage the maximum values of which are symmetrically disposed with respect to ground potential.
The generator may be an alternator and the higher voltage is produced by a winding which is centre-tapped to ground so as to reduce the peak voltage by a factor of the square-root of three with respect to ground. For efficiency reasons it is preferable to run the voltage supply circuit to the transformer at the highest acceptable safe levels as this minimises power losses in cables and components. The booklet xe2x80x98Memorandum of Guidance on the Electricity at Work Regulationsxe2x80x99 published by Health and Safety Executive, UK, 1990, page 21 suggests that safe operating voltages are 50 volts a.c. or 120 volts d.c. An additional benefit of running at the highest acceptable voltages is that size and weight of transformer are minimised as fewer windings are required due to the fact that the voltage step-up of the transformer is reduced.
In an alternative arrangement, the higher voltage output is produced as a d.c. voltage from one or more separate stator windings on the generator and in conjunction with a bridge rectifying circuit.